scholarly journals Microstructural Investigations of Ni-Based Superalloys by Directional Solidification Quenching Technique

Materials ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 4265
Author(s):  
Tobias Wittenzellner ◽  
Shieren Sumarli ◽  
Helge Schaar ◽  
Fu Wang ◽  
Dexin Ma ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Single Crystal ◽  
Cooling Rate ◽  
Electron Backscatter Diffraction ◽  
Local Concentration ◽  
Directionally Solidified ◽  
Polycrystalline Structure ◽  
Characterization Methods ◽  
Solidification Mechanism ◽  
Cast Microstructure

The improvement of the mechanical properties of Ni-based superalloys is achieved in most cases by modifying the chemical composition. Besides that, the processing can be modified to optimize the as-cast microstructure with regard to the mechanical properties. In this context, the present study highlights the solidification mechanism of several Ni-based superalloys by conducting experiments using a modified, laboratory-scale Bridgman-Stockbarger furnace. In that context, the single-crystal rods are partially melted, directionally solidified and quenched sequentially. Several characterization methods are applied to further analyze the influence of the alloying elements and the variation of the withdrawal rate on the as-cast microstructure. Four stages of solidification are distinguished whereby the morphology observed in the different stages mainly depends on the cooling rate and the local concentration of the carbide forming elements. The effect of carbide precipitation and the effect on the as-cast microstructure is investigated by employing energy dispersive X-ray spectrometry (EDX) and electron backscatter diffraction (EBSD) analysis techniques. A local polycrystalline structure is observed in the single-crystal system as consequence of the influence of the carbon content and the cooling rate. The present work aims to develop strategies to suppress the formation of the polycrystalline structure to maintain the single-crystal microstructure.

scholarly journals The Microstructure, Mechanical Properties and Coatability of Diffusion Brazed CMSX-4 Single Crystal

1996 ◽  
Author(s):  
Warren M. Miglietti ◽  
Ros C. Pennefather
Keyword(s):  
Mechanical Properties ◽  
Single Crystal ◽  
Elevated Temperatures ◽  
Aluminide Coating ◽  
Turbine Blades ◽  
Stress Rupture ◽  
Directionally Solidified ◽  
Diffusion Brazing ◽  
Brazed Joints ◽  
Boride Phases

Diffusion brazing is a joining process utilized both in the manufacture and repair of turbine blades and vanes. CMSX-4 is an investment cast, single crystal, Ni-based superalloy used for turbine blading and vanes, and has enhanced mechanical properties at elevated temperatures when compared to equiaxed, directionally solidified and first generation single crystal superalloys. The objective of this work was to develop a diffusion brazing procedure to achieve reliable joints in the manufacture of a hollow turbine blade (for a prototype engine in South Africa), and to verify the coatability of the diffusion brazed joints. Two commercially available brazing filler metals of composition Ni-15Cr-3.5B and Ni-7Cr-3Fe-4.5Si-3.2B-0.06C and a proprietary (wide gap) braze were utilized. With the aim of eliminating brittle centre-line boride phases, the effects of temperature and time on the joint microstructure were studied. Once the metallurgy of the joint was understood, tensile and stress rupture tests were undertaken, the latter being one of the severest tests to evaluate joint strength. The results demonstrated that the diffusion brazed joints could satisfy the specified stress rupture criterion of a minimum of 40 hrs life at 925 °C and 200 MPa. After mechanical property evaluations, an investigation into the effects of a low temperature high activity (LTHA) pack aluminide coating and a high temperature low activity (HTLA) pack aluminide coating on the braze joints was undertaken. The results showed that diffusion brazed joints could be readily coated.

scholarly journals Correlation between microstructure, thermal parameters and mechanical properties of a directionally solidified Al-1%wt Mn alloy

2018 ◽  
Author(s):  
Danilo Luvizotto Gonçalves ◽  
Noe Cheung ◽  
Ricardo Orcelio Miranda de Oliveira Junior
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Vickers Microhardness ◽  
Rolling Process ◽  
Thermal Parameters ◽  
Unsteady State ◽  
Directionally Solidified ◽  
Strength Tests ◽  
Cast Microstructure

This works aims to study the mechanical properties of a Al-1%wt Mn alloy directionally solidified under unsteady-state conditions. The as-cast microstructure was analysed by measuring the cellular spacing, and the mechanical properties were obtained through Vickers microhardness and tensile strength tests. The correlation between the mechanical results and the as-cast microstructure was fundamental to imply a relation between the solidification thermal parameters and the rolling process in which this kind of alloy is submitted to afterwards.

Identification and Evaluation of Freckles in Directionally Solidified Casting Made of PWA 1426 Nickel-Based Superalloy

2012 ◽  
Vol 57 (2) ◽  
pp. 559-564 ◽  
Author(s):  
B. Chmiela ◽  
M. Sozańska ◽  
J. Cwajna
Keyword(s):  
Mechanical Properties ◽  
Electron Backscatter Diffraction ◽  
Turbine Blades ◽  
Casting Defects ◽  
Directionally Solidified ◽  
Nickel Based Superalloy ◽  
Aero Engine ◽  
And Performance ◽  
Backscatter Diffraction ◽  
Equiaxed Grains

Identification and Evaluation of Freckles in Directionally Solidified Casting Made of PWA 1426 Nickel-Based SuperalloyManufacturing of modern aero engine turbine blades made of nickel-based superalloys is very complex and expensive. The thrust and performance of new engines must address constantly more demanding requirements. Therefore, turbine blades must be characterised by very good mechanical properties, which is possible only if the blades are free of casting defects. An important innovation has been the launching of directionally solidified (DS) and single crystal (SX) turbine blades. But, manufacturing procedures and the chemical composition of many superalloys promote the formation of casting defects that are characteristic only for directional solidification. One of these defects is freckles. Freckles are small equiaxed grains in the form of long chains parallel to the solidification direction and are located on the surface of the casting. Freckles decrease the mechanical properties of DS and SX blades; therefore, they should be always unambiguously identified to improve the manufacturing process. This work presents the possibilities of identifying and evaluating freckles in DS casting made of PWA 1426 superalloy by combining the scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and electron backscatter diffraction (EBSD) techniques.

Directionally Solidified DS CM 247 LC—Optimized Mechanical Properties Resulting From Extensive γ′ Solutioning

1985 ◽  
Author(s):  
G. L. Erickson ◽  
K. Harris ◽  
R. E. Schwer
Keyword(s):  
Mechanical Properties ◽  
Single Crystal ◽  
Turbine Blade ◽  
Incipient Melting ◽  
Directionally Solidified ◽  
Operating Condition ◽  
C 50

Complete coarse γ′ and greater than 90% eutectic γ-γ′ solutioning, without incipient melting, is demonstrated for the DS CM 247 LC superalloy. This unusual capability for this advanced Ni-base turbine blade and vane material results in considerable mechanical properties enhancement, with the DS alloy capability being near to current single crystal superalloys in the 345–207 MPa, 871°C–982°C (50–30 ksi, 1600°F–1800°F) operating condition. Microstructural features are detailed correlating strength and alloy stability.

The Influence of Deformation on Microstructure Evolution of Low Alloy TRIP Steel

2010 ◽  
Vol 638-642 ◽  
pp. 3531-3536
Author(s):  
Lucia Suarez ◽  
Josep Antonio Benito ◽  
Pablo Rodriguez-Calvillo ◽  
Daniel Casellas ◽  
Yvan Houbaert ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Retained Austenite ◽  
Electron Backscatter Diffraction ◽  
Physical And Mechanical Properties ◽  
Microstructural Characterization ◽  
Ferrite Matrix ◽  
Characterization Methods ◽  
Steel Microstructure ◽  
Trip Steels ◽  
Multiphase Microstructure

Low alloy transformation-induced plasticity aided (TRIP) steels have attracted much interest over the last years. TRIP steels were initially developed for automotive applications as they offer an excellent combination of strength and ductility at reasonable costs. These excellent mechanical properties mainly arise from a complex multiphase microstructure of a ferrite matrix and a dispersion of multiphase grains of bainite, martensite and metastable retained austenite. The relevant influence of microstructure on physical and mechanical properties makes metallographic study essential for an appropriate understanding and improvement of the mechanical behavior. An accurate microstructural characterization and quantification of the amount of the different constituents is indispensable to know how the stresses and strains are distributed within the different microstructural constituents. Among the different characterization methods commonly used electron backscatter diffraction (EBSD) appears to be the unique technique able to observe retained austenite grains often no larger than 1 μm. The present work shows the evolution of retained austenite while straining. Microstructural and textural evolution after different strains was examined by optical microscopy OM, EBSD and XRD techniques on TRIP800 steel. EBSD technique appears as a powerful tool for characterizing the complex multiphase steel microstructure and provides an accurate evaluation of the local crystallographic texture. It allows to measure orientation gradients within individual grains of each different phase. The distinction between some phases is observed.

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